Such a lighting device is known from US20120163027A1, for example embodied as an indoor luminaire. The intensity distribution of an indoor luminaire is carefully designed to meet conflicting criteria related to a.o.:
discomfort glare, i.e. disturbing luminaire brightness;
illumination uniformity, i.e. the even distribution of light at the illuminated area and in the room;
cost, i.e. the number of luminaires needed, optics type;
luminaire efficiency; and
luminaire utilization factor, i.e. the fraction of light of the total issued light on the right spot.
The desired intensity distribution is strongly dependent on the application details. For example, for recessed luminaires a broad intensity distribution is advantageous because it gives an even illumination at a relatively large luminaire spacing. A problem resides in that such an intensity distribution will lead to discomfort glare at higher-flux packages. For this reason, the flux package of a broad intensity luminaire is usually limited or has a higher glare rating classification, and beams with an intensity cut-off at large angles are used in applications where a larger flux package per luminaire is needed. Another example of a design trade-off is the ratio between direct (down) lighting and indirect (up) lighting with suspended luminaires. The direct lighting has a higher utilization factor and saves energy, but the direct light may become glary.
Discomfort glare is a feeling of discomfort caused by working under luminaires which are experienced as too bright, for example due to too bright light or too sharp transitions between dark and light areas in the space of the workplace. The cause and mechanism are not understood well, but the parameters influencing discomfort glare have been studied extensively. The difference in glare may be the result of parameters like the direction of the beam, sharpness of intensity cut-off, size of light-emitting area, sample area (i.e. area where the glare is measured, for example target or task area), etc. Although many measures of discomfort glare have been proposed in the past, the UGR (=Unified Glare Rating) is most widely accepted. The European standard for lighting of indoor workplaces EN-12464-1 prescribes UGR limit values for various working conditions, as well as minimum illumination levels. The UGR is expressed as:
  UGR  =      8    ⁢    log    ⁢          0.25              L        B              ⁢          ∑                          ⁢                                    L            2                    ⁢          ω                          p          2                    
wherein the summation is over all luminaires in the room, LB is the background luminance in the room, L is the luminance of the exit window of a luminaire, co is the angular extent of the exit window, and p is the Guth position index, p being relatively small for luminaires in the line of sight and relatively large for luminaires in the periphery of the visual field. In general, a high lumen output of the luminaire will lead to a higher light level in the room (larger LB) but also to a large exit window luminance L. The net effect is a higher glare rating. If the luminance of a dimmable luminaire at dim level a (0<α<1) is expressed as:L=αLmax 
The glare increases with dim level according to:
  UGR  =            8      ⁢      log      ⁢              0.25                  α          ⁢                                          ⁢                      L                          B              ,              max                                          ⁢              ∑                                  ⁢                                                            (                                  α                  ⁢                                                                          ⁢                                      L                    max                                                  )                            2                        ⁢            ω                                p            2                                =                  UGR        max            +              8        ⁢        log        ⁢                                  ⁢        α            
The strongest contribution to glare comes from luminaires that are viewed at a small angle to the horizon, because of the orientation close to the line of sight (expressed in the Guth position index) and because the number of visible luminaires is highest in that direction. Therefore, the most common approach to reduce glare is to create an intensity cut-off, such that the luminance of the luminaire in the abovementioned directions is kept low. Another approach is to reduce the overall luminance by creating a large light-emitting surface. This approach is frequently used in indirect lighting.
Light is able to elicit biological, non-visual effects. The effects depend on the time of day and the amount of light and the spectral composition. At night, light exposure suppresses the nocturnal production of the hormone melatonin; this hormone enables consolidated sleep. Light aligns and stabilizes the circadian rhythm and it aligns the sleep-wake cycle with the 24 hr light-dark cycle. Moreover, light exposure improves alertness and mood and can be used to treat depression. The biological effects of light increase with light intensity, and saturate beyond certain light levels. The mood and alertness improving action of daytime light exposure reaches saturation at relatively high illumination levels or light intensities, typically above 1500 lux (measured on a horizontal surface, lux is lm/m2 or cd·sr/m2). Such relatively high illumination levels need not be provided all day, but by providing short periods of bright light or intermittent bright light exposure similar effects result as those achieved after longer pulse durations. When such short, relatively high illumination level periods are realized within indoor lighting systems, care should be given that this does not compromise the visual comfort. High-illuminance lighting systems require special measures to prevent glare discomfort, disability and reflection glare, and unpleasant, uneven light distributions in the room. In addition to the need for high illuminance having positive non-visual effects as a benefit, high illuminance lighting systems are also desired for people with diminished vision due to e.g. the aging of the eye. It is well known that the needs of elderly as regards illumination conditions are stronger than those of young people, with respect to, for example, high intensity, glare-free (including reflection glare), homogeneous lighting distribution (low luminance contrasts in space) and, in the case of vision of fine details, contrast enhancement of, for example, the symbols.
In particular for lighting solutions that are used for general lighting as well as biological light therapy, for example circadian or dynamic lighting systems, a huge variation in light output and consequently intensity distribution is required. Presently, the known dimmable lighting devices have the disadvantage that the intensity distribution of a luminaire/light system is usually optimized for a specific flux package, but that the intensity distribution is not optimal for all dim levels. Another issue is the use of local presence detectors, which often results in the disadvantage of an unbalanced light distribution between dimmed up light at positions where office workers are present and dimmed down light at unoccupied areas. The dimmed-up luminaires have a different flux and a different function than the dimmed-down luminaires.